Safety switch mechanism



Nov. 8, 1927. L643 39 I. E. M CABE SAFETY SWITCH MECHANISM Filed Nov. 8, 1926 2 Sheets-Sheet 1 IN V EN TOR. RA E. M (SE35 ATTORNEYS.

Nov. 8, 1927. 1,648,390

I 1. E. M cABE SAFETY SWITCH MBCHANI SM Filed Nov. 8; 1926 2 Sheets-Sheet 2 INVEN TOR. IRA E. M CABE BY I Z5 I ATTORNEYS.

Patented Nov, 8, 1927.

UNITED STATES PATENT OFFICE.

ma 1:. McCABE, or cHIcAqo, ILLINOIS.

s rew, swrron. mncnnnrsmf This invention relates to improvements electrical switches and more particularly to the construction of'a temperature control safety switch mechanism.

In industries where high teinperaturesare used, such as in the reduction and treating of metals and wherever furnaces. are em ployed, requiring av high temperature, it is desirable and in some cases necessary to employ a control which will withstand the high temperatures employed. Most furnaces of this character employ an electrical circuit in connection with the production of theflame or source of heat such as an electricaL 1y operated liquid fuel burner and it is an object of this invention to, provide a safety control which will withstand the high temperature of thefurnace and positively act to break the electric circuit should the source of heatibe discontinued for any abnormal reason.

While the preferred form of this invention is illustrated on the accompanying sheets of drawing it is to be understood that minor detail changes may be made without de-;

of'mercury tube switch, which is not a part of this invention, as it is particularly adapted to ,be employed where the actuating element must necessarilyvbe subjected to intensely high temperatures, but the particular construction of the operating parts may-be actuated by other forms of thermal control switches. a

The device contemplated in accordance with this invention comprises a means for inountin the casing and the operating parts containe within such casing particularly adaptable for employment with a mercury tube switch which comprises a long glass tube or stem 1, closed at one end and terminating at the other end in a tubular membertrated preferably employs a particular type.

Application filed November 8, 1926. Serial No. 146,971.

2 of small diameter. The member 2'is bent downwardly, assuming'the stem to be horizontaliand then laterally at an acute angle to the vertical and again upwardly to form a V-shaped elbow 3. The vertical arm of the elbow terminates in a bulb or chamber 4 of considerable capacity. The members 1, 2, 3 and 4: may all conveniently be of glass formed intoone integral structure. Entering the top of the bulb'or chamber are leadingn wires 5, sealed in the glass; these leading-in wires being connected to the upper ends of a pair of long terminals or contact pieces 6 of iron or other suitable material. The members 6 are spaced apart I from each other and they extend down into the upper end of the vertical arm of the elbow 3. The leading-in wires are connected to external conductors 7 and 7. Within the elbow-is a small body of mercury 8 sufficient to form a seal, when the pressure on opposite sides thereof is the same, between the twoarms of the elbow The parts are so proportioned that when the'mercury is in a position of rest, such as shown in Fig. 2, the pressure in the stem and the chamber 4 being equal, there is a gap between the lower ends of the contact pieces and the top of the mercury; this being the open position 8 of the switch. If the pressure in the stem rises, assuming the device as a whole to be filled with a suitable gaseous medium, the

mercury will be caused to flow in a direction away from the stem and towardthe bulb 9" orchamber, risingin the'vertical arm of the elbow, and engaging with the contacts 6,.

thus completing the circuit of which the conductors 7 form a part. i I

This mercury tube switch is operated by inserting the stem 1 within the furnace, or

flue leading therefrom, and is usually formed of Pyrex or other glass of a type adapted to withstand high temperatures without cracking orbr'eaking. It is desira= ble to mount the casing containing the switch .mechanism co-operating with this' mercury tube switch at a distancevfrom the.

heat of the furnace which casing must necessarily support the bulb/i. In Figure 1,

the wallet the furnace or fiue leading t-herefrom to the stack is indicated by the reference numeral 9. A tubular casing 10 surrounding the stem 1 of the thermal switch is provided with a movable flanged sleeve 11 adapted to be secured thereto by a set screw and the flanges of which are adapted to be secured to the outer wallof the furnace or flue by any desired means that will rigidl support tubular casing 10 thereon, such as y the anchor bolts shown. The exterior end of the tubular. casing 10 terminates ata distance from the exterior wall of the furnace or flue in a circular shield 12 extending at right angles to the tubular casing. This shield supports a spaced-apart circular mechanism casing 13, preferably of less diameter, upon supporting posts let'secured' to both shield and mechanism casing, with the adjacent or rearwall 15 provided with an outstanding tubular casing 16 in alignment ing therefrom.

16 with the bulb 4 held in the proper posi-.

tion within the casing by engagement with a springclip 18' secured to the rear wall 15,

as shown in Figure 2. The tubular casing 10 is-of larger inner diameter than the thermal element 1 passing therethrough and 'opens through the shield to the atmosphere and through the wall 9 to the interior of the furnace or flue finding sufficient space there:

about to allow an induced draft of cool atmospheric air'to reduce the transmission of heat from the thermal element and casinglO ,to the mechanism casing 13. The parts cooperating with themercury switch above described preferably comprise another mercury tube switch 19 of a commercial type having two electrodes or terminals adjacent each a other and entering the switch tube adjacent one end, so that when the switch tube is tilted toward that end the mercury therein will close the circuit between the terminals and when tilted toward the other end themercury will'flow away and openthe circuit between said terminals. This mercury tube switch is carried in a frame rotatably mounted upon a shaft 20 secured to the rear wall of the casing which frame is provided with acounteriveight 21 arranged to normally tilt the switch tube 19 into the open circuit positiouand the counterweight or frame supporting it is provided with a projection 22 adapted to be engaged by an arm 23 of a manual reset shaft rotatably mounted on the rear Wall ofthe casing having a knurled knob 24 for manual engagement on the rear side thereof, so that upon the operation of the reset device the tubular switch 19 maybe rotated about its pivot to assume the closed position. To releasably hold the tilting switch tube 19 in closed position, an

abutment 25 is formed extending downwardly from the switch carrying'frame adapted I switch 19 in closed position. The engagement between the abutment and catch is preferably made by providing the lower end of the abutment with a set screw, or by bending the extremity at right angles toward the r'ear of casing wall. The catch 26 is of thermal character and preferably formed of a bimetal strip supported at its lower end in a clam 27 supported on the rear wall of the caslng and so constructed that upon an increase in temperature the upper free end of the catch will move toward the rear wall 15 of the casing and release the abutment to allow the counterweight 21 to rotate switch tube-'19 to the open position, and: when the temperature is reduced will allow the reset 24 to causethe abutment to wipe over the catch and be again engaged by it to hold the switch tube 19 in closed po-.

sition.

In order to apply heat to increase the temperature of the bimetal catch 26 to release the rotatable switch tube an electric. heating element 28 is attached thereto. This heating element comprises a cylindrical casing'28 insulated with mica or any other insulating material, carried upon the bimetal strip 26 by passing the strip through opposite walls thereof adjacent the rear end and arranging 'a plurality of compressible carbon or other resistance discs 29 within the casing in contact with each other and with the strip at one end and with a compression member 30,

which is insulated from the carbon discs by an insulating disc, at the other or outer and through which the pressure with which. the discs bear against each other ma be adjusted in an rotata le cap on the outer end of the casing having a spring finger 31 adapted to resiliently engage 1n a series of longitudinal notches 32 arranged about the exterior of the casing adjacent that end and holding the cap in place. I

-A. binding post 33 is preferably carried upon the clamp 27 which supports the lower end of the thermal catch .26 and forms an electrical connection with such strip. Two binding posts 34 and 35 are mounted upon and insulated from the rear wall 15 of the casing below the catch binding post 33.- The binding post 34 is connected by a lead 35 to the series of discs 29 adjacent the pressure block 30. One terminal 6 of the thermal actuated switch bulb 4 is connected to the binding'post 34 by a. lead. 7 and the other terminal 6 of this switch is connected by a lead 7 to the binding-post 33 upon the ther-;

Inn

desirable manner, pre erably by, a v

mal catch 26, which binding post 33 is in terminal catch is connected by a lead 37 to the binding post 35. The binding posts. 34

and 35 are connected by leads 38' and 38 I passing out throu h the bottomof the casing to the circuit to The terminals 6 within the bulb 4 of the thermally actuatedmercury tube switch are, therefore, in a shunt circuit -.which when closed by the mercury 8' within the. bulb t reduces the strength of the current of the 7 mercury tube switch 19 acts as a safety switch because, when the main circuit to the control is closed during the normal operation of the electrically operated heat producing device with which it is associated, and for any reason the device does not produce such heat or, having once done so it should then fail to continue such production, the circuit betweenterminals 6 in bulb 4 of the thermal switch will be broken by the reduction of the mercury 8 in bulb 4:, causing the full strength of the current of the main circuit to be caused to pass through the heating element mechanical means normall 28 and rotatable switch 19 and the heat generated thereby within the element 28 will be transmitted to the thermal catch 26 causing it to move out of contact with the abutment 25 and allow the counterweight 21 to rotate switch 19 to break the circuit therethrough" "in a shunt circuit mounted upon said catch.

During the normal operation of the electric heat producing device with which this device is adaptable to be employed the main circuit ma be opened and closed independv ently of t is device any number of times without affecting the operation of such device but when once the main circuit is broken within this device the heat producing device cannot be caused to operate until the. safety switch 19 has been moved by thereset 24 i'n'to'the closed position.

What I claim is:

1. A safety switch comprising a thermallg actuated switch and a mechanically actuated switch connected in series in the circuit to,

be controlled, said latter switch having acting to open said switch, and a releasa 1e catch to hold said switch in closed position provided with electric means in a shunt circuit for releasing said catch, said latter means provided with a manual adjustment to regulate the amount of the current passing therethrough, whereby when both switches are closed the current of the circuit to be controlled passes through e controlled.

erate the switch to break both switches, and'when the thermally actuthrough. v i

2. A" safety switch comprising thermally actuated and mechanically actuated switches in series in the circuit to 'be controlled, said latter switch having mechanical means normally acting to open said switch, and a releasable catch to hold said switch in closed position having a manually-adjustable electric means in a shunt circuit for releasing said catch, whereby the amount of the currentipassing through the shunt may be regulated to adapt the safety switch quickly to ,various strengths of current of the main circuit after assembling the device.

3. A safet switch com rising a thermall actuated an a mechanica ly actuated switc in series in the circuit to be controlled, a

thermally actuated catch adapted to hold the latter switch in closed position, and a heating element co-operating therewith in a shunt circuit-with said switch comprising a plurality of super-imposed resistance discs in said shunt circuit and manual means in connection therewith to vary the' pressure with which said discs bear against each other.

4. A safety switch comprising aplurality .of switches in series in the circuit to be controlled, includinga mechanically o erated switch,said latter switch having mec anical meansnorm'ally acting to open said switch, a thermally actuated releasable catch normally holdlng said switch in closed position, and a manually adjustable heating element closed position, comprising a bi-metal strip the circuit there and a manually adjustable electrical resistance element controlling the amount of the current required to generate sufficient heat to actuate the thermal catch to release the mechanically operated switchin the main circuit. l 6. A safety'switch comprisinga thermally actuated switch and a mechanically operated I switch in series in the circuit to be controlled mounted in a casing in connection with a thermally actuated releasable catch for the latter switch in'a shunt circuit, the thermal member of said first switch passing through and extending beyond said casin and adapted to be extended within the wafis surrounding a heat producing element, means surrounding said thermal member adapted to be secured to said Walls and supporting at a distance therefrom a shield for said casing, and meansv carried upon the shield to support the casing at a distance therefrom and from the said means surrounding the thermal member.

7. A safety switch comprising a thermally actuated switch and a mechanically operated switch in series in the circuit to be controlled, mounted in a casing in connection with a thermally actuated releasable catch for the latter switch in a'shunt circuit, the thermal member of said first switch passing through and extending beyond said casing and adapted to be extended within the walls surrounding a heat producing element, means surrounding said thermal member adapted to be secured to said walls and supporting at a distance therefrom a shield for said casing, means carried upon .the shield to support the casing at a distance therefrom and from the said means surrounding the thermal member, and resilient means mounted. within the casing and mounted within the shield supporting means to yieldably en gage and positionthe thermal member extending therethrough.

8. A safety switch comprising a thermally actuated switch and a mechanically operated switch in series in the circuit to be controlled, mounted in a casing in connectionwith a thermally actuated releasable catch for the latter switch in a shunt circuit, the thermal member of said first switch passing through andextending beyond said casing and adapted to be extended within the walls surrounding a heat producing element, means surrounding said thermal member adapted to be secured; to said walls and supporting at a distance therefrom a shield for said casing, means carried upon the shield to support the casing at a distance therefrom and from the said means surrounding the thermal member, the means surrounding the thermal element between the walls and shield forming a draft conduit from the shield into the heat producing element for reducing transmission of heat from the heat elements to the mechanism casing.

IRA E. MoCABE. 

